Chemistry Reference
In-Depth Information
12.
Predict the product expected from electrophilic aromatic substitution reactions of
pyrrole, furan, and thiophene.
13.
Write the mechanism of electrophilic aromatic substitution reactions of pyrrole, furan,
and thiophene.
14.
Explain why pyridine is less reactive than benzene in electrophilic aromatic
substitution reactions.
15.
Explain why pyrrole, furan, and thiophene are more reactive than benzene or
pyridine in electrophilic aromatic substitution reactions.
16.
Predict the products expected from treatment of pyridine and imidazole with
Brønsted-Lowry acids and electrophiles such as iodomethane.
ANSWERS TO PROBLEMS
Problems Within the Chapter
13.1
a.
-
N
+H
2
S
O
4
NHHO
4
S
+
b.
-
N
+
HO
3
N
NH
N
O
3
+
13.2
The contributors to the resonance hybrid derived from electrophilic attack at C-2 are:
+
+
E
E
E
+
N
N
N
H
H
H
The contributors to the resonance hybrid derived from attack at C-4 are:
HE
HE
HE
+
+
+
N
N
N
In each case, positive charge is placed on the nitrogen atom in one resonance
contributor. This is a destabilizing effect due to the electronegativity of nitrogen.
Electrophilic attack at C-3 gives a cation in which the positive charge does not reside
on nitrogen (see Example 13.1). Therefore, attack at C-3 is favored relative to attack
at C-2 and C-4.
